The present invention generally relates to a communication system having two opposed data processing units each having a function of monitoring the other data processing unit.
There is known a communication system having two microprocessor units which are coupled to each other through a data link line. The microprocessor units each control respective devices such as multiplexers. A hand held monitor is provided for each of the microprocessor units. The operator can access the microprocessor unit through the associated hand held monitor. When the operator on the side of one of the microprocessor units wishes to obtain data relating on the other microprocessor unit or its peripheral device such as a multiplexer, the operator inputs an instruction to the microprocessor unit of its own through the associated hand held monitor. The input instruction is converted into a conventional format under the control of a central processing unit of the microprocessor unit on the operator side, and is then transmitted to the other microprocessor unit through the data link line. The other microprocessor unit analyzes the received instruction and generates requested data. Then the other microprocessor unit converts the same into a conventional format and sends the requested data to the microprocessor unit on the operator side through the data link line. The central processing unit of the microprocessor unit on the side of the operator analyzes the received requested data and provides the operator with an indication based on the requested data through the hand held monitor. Thereby, the operator on the side of one of the microprocessor units can monitor the status of the other microprocessor unit or devices controlled thereby.
It is noted that a processing of the central processing unit on the operator side is needed to obtain data on the other microprocessor unit or its peripheral device. As described previously, the central processing unit on the side of the operator converts the input instruction into the conventional format and analyzes the received data assembled in the conventional format. Such a processing is a load of the central processing unit. When the central processing unit has a sufficient operating capacity, there is no problem even when the above-mentioned processing is executed. However, when the central processing unit is operating with a heavy load, the operating speed is decreased so that services provided by the microprocessor unit are degraded. For example, it takes a long time to obtain data on the other microprocessor unit.